The development of plasma enhanced processes for deposition, etching, cleaning, and surface treatments have been instrumental to maintain the progress in many manufacturing industries, such as, integrated circuits (IC), liquid crystal display screens—both LCD and OLED—and photovoltaic (PV) cells or panels.
Example reactors for plasma enhanced processing include parallel plate capacitive, sputtering and microwave discharge reactors. Scaling such reactors to process ever larger substrates typically makes it difficult to maintain desired film properties and uniformity. Further, coatings applied using such technologies have general characteristics, strengths and limitations which make them more or less suitable for different types of applications. Typically, sputtering makes coatings that have more columnar structure and less dependent on substrate temperature for proper composition of the film. RF plasma-based PECVD on the other hand tends to make denser films with more controllable stress and amorphous structure but it requires substrate temperatures above about 180 Celsius. Microwave deposition typically produces coatings at a higher rate and more efficiently from the gas feedstock but the coatings tend to be less adherent. Regarding the cleanliness of the respective technologies—RF-plasma-based PECVD has demonstrated best performance in semiconductor manufacturing of nanometer scale devices with zero defects above about 200 nm size on wafers of 300 mm diameter.
Currently, there are a growing number of opportunities for new coatings for purposes such as chemical barriers, scratch protection or optical functions on plastic substrates or on polymer layers. Some commercial applications are:
Backside insulation for thinned silicon wafers in 3D wafer level packaging. This is currently used mainly for image sensors but will be used in the next 5 years for high speed IC packaging for computing and network devices. Passivation layers for image sensors, both for concentrator lenses and for dye-based color filters. Hard coating for plastic panels used for many purposes such as unbreakable windows or scratch resistant panels for solar concentrating PV modules—including highly transparent plastics: acrylics, PMMA, PPSU, PC, and PETG.
In some important applications such coatings must be ultra-clean, which means very low defect levels—approximately one per square meter—in order to produce very large TV screens which are one of the high value products. Such substrates often cannot tolerate the minimum temperatures, typically upwards of 200 degrees Celsius, required by all PECVD reactors for ultra-clean coating processes such as depositing hard, impermeable dielectric films. While sputtering can easily provide films at substrate temperatures less than 100° C. the coatings which are applied typically are not impermeable and may be flaky due to generally tensile stress. Particle defect levels are also much higher in sputter coaters due to the difficulty of in-situ cleaning. Being able to make a high quality dielectric (hard) coating on such plastic or organic polymers is a very important industrial process enabling a number of high-potential mass market products to be manufactured at reasonable cost.